1. Technical Field of the Invention
The present invention relates to photoprotective compositions for topical application containing a dibenzoylmethane derivative, an oil containing in its structure at least one amide unit more fully described hereinbelow and a compound capable of accepting the excited triplet level energy of the said dibenzoylmethane derivative.
The present invention also relates to a process for photostabilizing at least one dibenzoylmethane derivative against UV radiation via a combination of a an amide oil compound and a compound capable of accepting the excited triplet level energy of the said dibenzoylmethane derivative.
2. Description of Background and/or Related and/or Prior Art
It is known that light radiation with wavelengths of from 280 nm to 400 nm permits tanning of the human epidermis and that light rays with wavelengths more particularly from 280 to 320 nm, known as UV-B rays, cause skin burns and erythema which can harm the development of a natural tan. For these reasons, as well as for aesthetic reasons, there is a constant demand for means of controlling this natural tanning in order thus to control the color of the skin; this UV-B radiation should thus be screened out.
It is also known that UV-A rays, with wavelengths from 320 to 400 nm, which cause tanning of the skin, are liable to induce adverse changes therein, in particular in the case of sensitive skin or skin which is continually exposed to solar radiation. UV-A rays cause in particular a loss of elasticity of the skin and the appearance of wrinkles leading to premature aging of the skin. Same promote triggering of the erythemal reaction or amplify this reaction in certain individuals and may even be the cause of phototoxic or photoallergic reactions. Thus, for aesthetic and cosmetic reasons such as the conservation of the skin's natural elasticity, for example, an increasingly large number of individuals wish to control the effect of UV-A rays on their skin. It is thus desirable also to screen out UV-A radiation.
For the purpose of protecting the skin and keratin materials against UV radiation, anti-sun/sunscreen compositions comprising organic screening agents that are active in the UV-A range and in the UV-B range are generally employed. The majority of these screening agents are liposoluble.
In this respect, one particularly advantageous family of UV-A screening agents currently consists of dibenzoylmethane derivatives, and in particular 4-tert-butyl-4′-methoxydibenzoylmethane, which are liposoluble and have high intrinsic absorbing power. These dibenzoylmethane derivatives, which are compounds which are now well known per se as screening agents that are active in the UV-A range, are described in particular in FR-A-2,326,405 and FR-A-2,440,933, as well as in EP-A-0,114,607; 4-tert-butyl-4′-methoxydibenzoylmethane is moreover currently marketed under the trademark “Parsol 1789” by Roche Vitamins.
Unfortunately, it has been found that dibenzoylmethane derivatives are compounds that are relatively sensitive to ultraviolet radiation (especially UV-A), i.e., more specifically, they have an annoying tendency to be degraded more or less quickly under the action of this UV. Thus, this substantial lack of photochemical stability of dibenzoylmethane derivatives towards ultraviolet radiation, to which they are by nature intended to be subjected, does not make it possible to ensure constant protection during prolonged exposure to the sun, and so the user must make repeated applications at regular and close time intervals in order to obtain effective protection of the skin against UV rays.
To solve this technical problem, it has already been proposed in the prior art to combine dibenzoylmethane derivatives with compounds capable of accepting the excited triplet level energy of the said dibenzoylmethane derivative. This is the case, for example, for the naphthalene derivatives in U.S. Pat. Nos. 5,993,789, 6,113,931, 6,126,925 and 6,284,916. This is also the case for the fluorene derivatives as described in U.S. Published Application Nos. 2004/0057912, 2004/0057914, 2004/0057916 and 2004/06272. However, the photochemical stability of the dibenzoylmethane derivatives obtained with these compounds is still not fully satisfactory.